Grooved power transmission belt.

The invention relates to power transmission belts of the type with inner surface "striated", that is to say comprising tries or circumferential ribs.

These belts have specific geometric shapes that meet standards such as DIN 7867 standard or the draft ISO R 15-506 standard. They are used especially in the automotive and household appliances (driving a drum washing machine or tumble dryer for example) and can have streaks truncated summit, which in cross section a trapezoidal shape.

It was found that a belt of this type has often after a certain length of service, cracks at the connecting edges between the small bases and the sides of the trapezoidal section streaks. These cracks are due to stress concentrations on the edges by contact with the sides and streaks edges with the corresponding surfaces of the pulleys on which the belt passes, and they result in the deterioration or the rapid destruction of the belt.

The present invention is intended to avoid this drawback of known belts and, as a corollary, to extend their lifespan.

It proposes to this end a grooved power transmission belt, internal surface including circumferential ridges or ribs with a truncated apex, having in cross section a substantially trapezoidal shape, characterized in that the small base of each rib has a surface concave curved and is connected to the flanks of the ridge by convex curved surfaces.

This replacement of the connecting edges between two planar surfaces in the grooves of the prior art belts, by convex curved surfaces, has the effect of reducing, to a large extent, stress concentrations in these areas. It follows, as a corollary, an increase in the life of the belts, which can reach 50%.

In addition, the concave shape of the small base streaks has the effect of changing the distribution of pressure on the flanks of ridges, on contact with the pulleys in a manner favorable to the reduction of stress on the flanks.

According to another characteristic of the invention, the convex curved surfaces have, in cross section, a radius of curvature between 0.2 and 2 millimeters, depending on the dimensions of the ribs, and they consist preferably of torus portions circular section.

The radius of curvature in a cross section of the concave surface may vary between 0.5 and 100 millimeters, depending on the size of the belt.

Preferably, this concave surface is connected directly to convex surfaces linking with the flanks of the ridges.

The invention will be better understood and other details, features and advantages thereof will appear more clearly on reading the following description, given by way of example with reference to the accompanying drawings, in which:<ul><li>- Figure 1 is a sectional perspective view of a ribbed belt of the prior art;</li><li>- Figure 2 is a half sectional view of a rib of a belt according to the invention.</li></ul>

There is shown, by way of example, in Figure 1, a V-ribbed belt according to the prior art, generally signed by the reference 10 and comprising an inner longitudinal reinforcing cords 12 embedded in elastomeric material 14 such as a rubber or a rubber mixture, of the type usually used for the manufacture of power transmission belts.

The outer face 16 of the belt 10 is substantially flat or smooth, while its internal surface is formed with serrations or circumferential ribs 18 with a truncated apex, which therefore have in cross section a substantially trapezoidal shape comprising a small base 20 connected to two oblique flanks 22 by edges 24.

When the belt 10 is activated and it passes over a pulley, the flanks 22 of the grooves 20 are applied on corresponding surfaces of parallel grooves of the pulley, and it is growing at the edges 24 a stress concentration resulting the formation of cracks and cracks leading to the destruction of the belt.

The invention avoids these drawbacks by giving each streak the particular form shown in larger scale in Figure 2.

In this figure, which is a half-sectional view of a rib of a belt 30 according to the invention, the same type as the belt 10 of Figure 1, the small base 40 of each rib 38 is connected to the flanks 42 of the ridge by a convex curved surface 44 which is for example a portion of circular section torus, so that this surface 44 is shown, on the half-sectional view of Figure 2, by a circular arc.

Depending on the dimensions of the belt 30 and those of the ridges 38, the radius of curvature R1 of the convex surface 44 can vary from 0.2 to 2 mm, being for example 0.4 mm when the height of the ridge is about 2 millimeters.

These convex curved surfaces 44, which replace the sharp edges 24 of the belts 10 of the prior art, have the effect that the stresses in contact on a groove 46 of pulley shown schematically in Figure 2, are provided on the sidewall 42 and are less concentrated on the surface 44. This prevents the primers cracks or cracks that appeared at the edges 24 in the prior art, after a certain period of operation of the belt.

May indicate, for example, that the stresses in the convex curved region 44 are divided by a factor of about 2, all other things being equal.

To further reduce the stress concentrations in this area, the invention provides that the small base of each rib 38 is formed by a concave curved surface 40 whose radius of curvature R2 in cross-section, may vary between 0.5 and 100 mm depending on the dimensions of the belt and of the striations 38. the radius of curvature R2 is for example 2 mm when the height of a ridge 38 is approximately 2 millimeters.

The curved surface 40 forming the small base of each rib is connected directly to the curved surfaces 44 connecting with the flanks 42, so that the profile of each rib 38 is curved continuously, having an inflection point 48 between each convex surface 44 and concave surface 40.

As the convex surfaces 44, the concave surface 40 may be formed by a portion of circular section torus and then be shown, in Figure 2, by a circular arc.

The presence of the concave curved surface 40 to the base of each groove 38 has the effect of modifying the pressure distribution on the flanks 42 of the grooves in the portion on the pulleys, in a direction tending to reduce the stresses in the curved regions convex 44.

In general, the invention can increase the service life of the drive belts of this type, a value of up to 50%, thanks to a simple change in the form of part streaks. Moreover, this form of the invention is in favor of reducing the noise caused by the passage of the belt on the pulleys, thanks to the presence of the side air outlet channels formed at the base streaks by surfaces curved above.